Evolution • Chapter 15
Evolution • http://www.pbs.org/wgbh/evolution/educators/teachstuds/svideos.html
Evolution • Is it correct to say that Evolution is just a theory? Is gravity just a theory? Defend your answer.
Biological Evolution • All the changes that have transformed life on Earth from the earliest beginnings to the diversity of organisms in the world today. • Unifying theme of biology.
Biological Evolution • Microevolution: evolution on a small scale, affecting a single population. • Macroevolution: evolution on a large scale affecting changes in species across populations.
Charles Darwin • 1809-1882 • Darwin boarded the HMS Beagle in 1831. • Darwin’s role on the ship was as a naturalist and companion to the captain. • Darwin collected biological and geological specimens during the ship’s travels. http://en.wikipedia.org/wiki/Charles_Darwin
Charles Darwin http://en.wikipedia.org/wiki/Charles_Darwin
Charles Darwin • Over the 5 year-voyage, Darwin collected rocks, fossils, plants, and animals. • Darwin also read Charles Lyell’s Principles of Geology which influenced his thinking about the age of the Earth.
Charles Darwin • In 1835, the Beagle arrived in the Galapagos Islands. • This is where Darwin collected many new specimens and began to observe the differences in the varieties of animals among the different islands. • Darwin was intrigued with species diversity and conceived his theory of natural selection in 1838.
Natural Selection • Darwin’s theory had 4 basic principles that explained how traits of a population can change over time. • 1) Individuals in a population show differences or variations • 2) Variations are inherited • 3) Organisms have more offspring than can survive on available resources. • 4) Variations that increase reproductive success will have a greater chance of being passed on.
Natural Selection • Results in changes in the inherited traits of a population over time. • These changes increase a species’ fitness in the environment. • 4 Main Principles • 1) Overproduction of offspring • 2) Variation • 3) Adaptation • 4) Descent with Modification
Natural Selection • Variation exists within the inherited traits of the individuals. • An organisms phenotype may influence its ability to find, obtain, and utilize its resources and might affect the organisms ability to reproduce. • Phenotypic variation is controlled by the organisms genotype and environment.
Natural Selection • Adaptation leads to the increase in frequency of a particular structure, physiological process, or behavior in a population or organisms that makes the organism better able to survive and reproduce. • Fitness: used to measure how a particular trait contributes to reproductive success.
Natural Selection • Overproduction of offspring: The ability of a population to have many offspring raises the chance that some will survive but also increases the competition for resources.
Overproduction • Average cardinal lays 9 eggs each summer, if each baby cardinal survived and reproduced, it would take only seven years for the first pair to have produced one million birds. http://www.fcps.edu/islandcreekes/ecology/northern_cardinal.htm
Natural Selection • Descent with modification: as the environment of a population changes, the entire process of natural selection can yield populations with new phenotypes adapted to new conditions. • Each successive living species will have descended, with adaptations or other modifications, from previous generations.
Descent with Modification http://readingevolution.com/evolution.html
Descent with Modification http://readingevolution.com/evolution.html
Natural Selection • http://www.pbs.org/wgbh/evolution/educators/teachstuds/svideos.html
Natural Selection • What are the 4 components of Natural Selection? How does Natural Selection affect Hummingbird populations?
Why Does Evolution Matter? • http://www.pbs.org/wgbh/evolution/educators/teachstuds/svideos.html • Why is the theory of evolution important to doctors and the field of medicine? How does it affect the way illnesses and treatments are approached?
Continuity of Life • Recall: • All life that has existed on Earth share at least the same 2 structures, Nucleic Acids (DNA and RNA) and Protein.
Continuity of Life • Recall: • All ecologically successful organisms have reliable means of passing genetic information to offspring through reproduction. • Sexual Reproduction: 2 parents, meiosis, gametes. • Asexual Reproduction: 1 parent, genetically identical offspring.
Continuity of Life http://csls-text.c.u-tokyo.ac.jp/active/12_01.html
Continuity of Life • The genetic view of evolution includes the transfer of genetic material through reproduction. • The continuity of a population/species depends on the process of reproduction.
Mechanisms of Evolution • Population Genetics • Natural Selection • Molecular Biology
Population Genetics • Genetic Drift is the random change in the frequency of alleles of a population over time. • In large populations enough alleles “drift” to ensure the allelic frequency of the entire population remains constant from generation to generation. • In smaller populations the effects of genetic drift become more pronounced and the chance of losing an allele becomes greater.
Population Genetics http://legacy.hopkinsville.kctcs.edu/sitecore/instructors/Jason-Arnold/VLI/Module%203/Module3Evolution/Module3Evolution7.html
Population Genetics • Founder Effect • Extreme example of genetic drift. • Occurs when a small sample of a population settles in a location separated from the rest of the population. • Alleles that were uncommon in the original population might become common in the new population.
Population Genetics • Founder Effect • Amish Communities • 6-Finger Dwarfism http://www.teachersdomain.org/resource/tdc02.sci.life.gen.foundereffect/
Population Genetics • Bottleneck • Occurs when a population declines to a very low number and then rebounds. • The gene pool of the rebound population is often genetically similar to that of the population at its lowest level, reduced diversity.
Population Genetics • Bottleneck • Cheetahs • European Bison http://www.bio.miami.edu/ecosummer/lectures/lec_causesofevolution.html
Population Genetics • Gene Flow • The movement of genes into or out of a population. • Occurs during the movement of individuals between populations which increases genetic variability.
Gene Flow • Migration http://evolution.berkeley.edu/evosite/evo101/IIIC4Geneflow.shtml
Population Genetics • Nonrandom Mating • Limits the frequency of the expression of certain alleles while increasing the frequency of expression of other alleles. • Organisms usually mate with individuals in close proximity which promotes inbreeding and leads to changes in allelic proportions that favor homozygous individuals.
Nonrandom Mating • Mating preferences http://biology.unm.edu/ccouncil/Biology_203/Summaries/PopGen.htm
Population Genetics • Mutations • Increase the frequency and types of allele changes within populations (genetic variability). • Provide raw material for which natural selection works.
Population Genetics • Mutation • Resistant Lice http://evolution.berkeley.edu/evosite/evo101/IIIC1aRandom.shtml
Population Genetics • Hardy-Weinberg Principle • When there is no change in the allele frequencies within a species, a population is said to be in genetic equilibrium. • p + q = 1
Population Genetics • Hardy-Weinberg Principle: there are 5 conditions required to maintain genetic equilibrium • 1) Population must be large with no genetic drift occurring • 2) No movement in or out of a population • 3) Must be random mating • 4) No mutations within the gene pool • 5) Must be no natural selection.
Natural Selection • Acts to select individuals that are best adapted for survival and reproduction. • Three main ways natural selection alters phenotypes: • 1) Stabilizing selection • 2) Directional selection • 3) Stabilizing selection
Stabilizing Selection • Eliminates extreme expressions of a trait when the average leads to higher fitness. http://www.mun.ca/biology/scarr/Stabilizing_Selection_in_Humans.html
Directional Selection • Occurs when an extreme version of a trait makes an organism more fit. http://avonapbio.pbworks.com/w/page/9429288/Ch-23